Delamination strength of YBCO coated conductors under transverse tensile stress**Contribution of NIST, a US Government Agency, not subject to copyright.

Abstract

We present a new experimental technique to measure the delamination strength under transverse tensilestress of YBa2Cu3O7−δ coated conductors for electric power applications. The delamination strength, defined asthe tensile stress at which the ceramic layers delaminate from one another, is measured at76 K for different sample configurations. The delamination strength is reduced by as muchas 40% when the conductor is slit to smaller width, a standard fabrication process, and thisreduction is due to damage to the ceramic layers near the edges of the conductor. We foundthat the delamination strength of slit coated conductors can be raised significantly byreinforcing the conductor by laminating it with copper strips and adding solder fillets atthe edges. In relatively strong conductors, where the delamination strength is ashigh as 15 MPa, the critical current does not degrade before actual delamination.This fact greatly simplifies sample characterization of practical high-strengthconductors, since only mechanical measurements need to be made. The criticalcurrent does, however, degrade significantly as a function of transverse stress beforedelamination in weak conductors that have relatively low delamination strength below15 MPa. We discuss how a soft metallic layer in YBCO coated conductors may limitthe transverse stress that the superconducting layer experiences in applications.